The introduction of new low-k and ultra-low-k dielectrics into chip manufacturing poses new challenges for chemical mechanical planarization (CMP). Since the mechanical strength of low-k and ultra-low-k materials is relatively low, the mechanical force applied during CMP can fracture or delaminate low-k films from wafer substrates. Consequently, CMP is moving towards employing its polishing equipment with lower down forces, i.e. forces of or less than 3 psi (20.7 kPa). Operating the polishing equipment with lower down forces requires the polishing slurries to possess an increased removal rate to facilitate acceptable wafer throughput rates.
Another challenge facing slurry manufacturers is that the current low-k/ultra-low-k integration architectures are extremely diverse and largely depend on user-specific targets. Some relatively simple integration schemes will use conventional CMP slurries that have a low selectivity to the dielectric material. Although these slurries have good topography correction capabilities, they tend to induce excessive dielectric and metal losses. In addition to this issue, because of the higher aspect ratio of the metallized trench/via structures, some integration schemes will require higher selective slurries for decreased metal losses during barrier CMP. Furthermore, the potential for including capping layers of different films in integration schemes provides an extra level of complexity.
In addition to the difficulties arising from complex integration schemes, most ultra-low-k materials are porous and prone to slurry contamination. Depositing a porous capping layer on top of the porous dielectric prevents the slurry from contaminating the low-k film. In addition to this, current ultra-low-k integration schemes may contain multiple capping layers. For example, many ultra-low-k integration schemes employ two capping layers, a top sacrificial layer and an underlying bottom cap that protects the dielectric. For these two capping layer schemes, barrier low-k slurries must remove the barrier, maintain or correct topography from the previous steps, remove a sacrificial top capping layer and maintain the bottom capping layer with no “punch-through” to the underlying ultra-low-k. This requires selectivity control between several different films, barrier layers, one and possibly two capping materials, interconnect metals such as copper, and low-k dielectric films. Consequently, there is a demand for a slurry having the ability to control the selectivity between the barriers, dielectric, Cu films, and capping layers.